Semiconductor devices include metal layers that are insulated from each other by dielectric layers. As device features shrink, reducing the distance between the metal lines on each layer, capacitance increases. The parasitic capacitance may contribute to effects such as RC delay, power dissipation, and capacitively coupled signals, also known as cross-talk. To address this problem, insulating materials that have relatively low dielectric constants (referred to as low-k dielectrics) are being used in place of silicon dioxide (and other materials that have relatively high dielectric constants) to form the dielectric layer that separates the metal lines.
Attempts have been made to lower the dielectric constant by increasing the porosity of dielectric materials. For example, some porous dielectric materials use thermally activated porogens. When heat is applied, the porogen may decompose and/or volatize, leaving pores in the dielectric material. Lower dielectric constants are possible because the pores are voids having dielectric constants near one (1).
Pores in dielectric materials typically have been generated by thermal processing. For example, one such dielectric material is a silsesquioxane matrix containing porogens, which may be spun on to the substrate. Heating the material causes the porogen to decompose and vaporize, leaving pores in the dielectric layer, thereby decreasing the dielectric constant of that layer.
However, heating during other process steps can cause a porogen to decompose prematurely. For example, other process steps that require thermal input (such as photoresist bake and ashing steps or subsequent deposition steps for dielectric etch stop or metallic layers), may thermally decompose the porogen, resulting in various problems. Premature thermal decomposition of porogens, for example, can result in rough sidewall surfaces of metal interconnects. Additionally, some porogens, such as those based on poly(ethylene oxide) or similar materials, may be lost prematurely due to resist cleans that can attack or solubilize the porogen.
A porous dielectric material is needed that will not decompose prematurely during process steps that occur at high temperatures. A method of providing a porous dielectric material having a low dielectric constant is needed. A dielectric material and method is needed that will not be susceptible to premature decomposition of porogens, for use in forming dual damascene and similar interconnects in increasingly smaller semiconductor device geometries.